Comparison of In-vitro Activities of Linezolid and Vancomycin against Staphylococcus aureus Isolated from A Tertiary Care Hospital

BACKGROUND: Methicillin resistant Staphylococcus aureus (MRSA) has emerged as one of the commonest cause of hospital acquired infections worldwide. Vancomycin is the antibiotic of choice for treatment of MRSA, but due to slow increase in vancomycin minimum inhibitory concentration (MIC) (vancomycin creep),Vancomycin has become a suboptimal therapeutic option in critically ill patients. Linezolid has emerged as an alternative drug in the treatment of such cases. AIM: To compare in vitro activities of linezolid and vancomycin against Staphylococcus aureus, in order to help in formulating a better treatment. METHOD: 200 strains of Staphylococcus aureus were isolated from different clinical specimens between April 2010 to March 2011. Antibiotic sensitivity testing was performed by Kirby Bauer disc diffusion method and MICs of vancomycin and linezolid were determined for all 200 strains by agar dilution method by following CLSI guidelines. RESULTS: Among 200 strains, MIC for linezolid was 4 μg/ml for 3 strains, MIC was 2 μg/ml for 71 strains, and MIC was 1 μg/ml for 126 strains, while for the same 200 strains of Staphylococcus aureus, MIC of vancomycin was 4 μg/ml for 8 strains, it was 2 μg/ml for 103 strains and it was 1 μg/ml for 89 strains. CONCLUSION: Linezolid and vancomycin had similar in-vitro efficacies for Staphylococcus aureus in disc diffusion method, but the number of strains with higher ranges of MICs of vancomycin (1-4 μg/ml) were more as compared to those which had higher ranges of MICs for linezolid. So, we suggest that linezolid can be a good alternative for the treatment of multidrug resistant Staphylococcus aureus as compared to vancomycin.